The present invention relates to an active voltage probe for an electronic measurement instrument.
Active voltage probes provide a better method of coupling high speed signals to an electronic measurement instrument, such as an oscilloscope or a logic analyzer, than passive probes can provide. The active voltage probe has higher input impedance with less attenuation than a passive voltage probe. Its use extends the measurement capabilities of the probe-instrument combination. There are two types of active voltage probes: (1) a cathode follower probe and (2) a source follower probe, with the source follower version being more popular.
Conventional active voltage probes have three basic parts; a probe head, a cable and termination box. The probe head includes a source follower amplifier to receive a signal from a probe tip, and an output from the source follower is transmitted to an output amplifier of the termination box through the cable. Since the active devices of the probe head receive power from the termination box through an additional conductor in the cable, the conventional active probe is bulky in construction. Moreover, both signal and power voltage connectors are needed on a panel of the measurement instrument. When many probes are necessary to simultaneously measure a plurality of parameters of components such as integrated circuits, it is difficult to connect the required probes to the test points or component leads in a compact area, and hence more panel area of the instrument is necessary for the power voltage connectors. In addition, prior art probes are not isolated from instrument ground and therefore cannot measure a voltage (floating voltage) with respect to non-zero reference voltage.